Method and means for operating fluorescent lamps



June 15, 1948. A. P. FOSTER ,4 3

METHOD AND MEANS FOR OPERATING FLUORESCENT LAMPS Filed Jan. 25, 1946 IN V EN TOR.

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Patented June 15, 1948 UNITED STATES OFFICE;

METHOD AN D MEAN S FOR OPERATING FLUORES CEN T LAMPS Arnot. P. Foster, Cincinnati, Ohio- Application January 25, 1946,- SerialNo. 643,404

(Cl. 3l'5 '12;7.)a

10 Claims. 1

My invention relates to the problems inherent in the operation of a plurality of fluorescent light sources in such a way that the arc discharges in the various sources occur out of phase with each other, whereby the stroboscopic effect is substantially cut down. It has been hitherto proposed to operate a pair of fluorescent lamps with an inductive ballast for one and a modified ballast (usually capacitative, or involving capacitance) for the other, to gain this end.

In such installations it is uneconomical to provide separate transformation as well as separate ballast means for each lamp. But an attempt to use transformation common to a plurality of light sources involves certain problems. The transformer structures become elaborate, having usually a separate secondary for each light source, although a common primary may be used with certain types of magnetic cores.

Moreover, the core and the windings have to be made heavy and massive to take care of the disturbance of the power factor which occurs when one of the light sources ceases to function. These factors make the control-circuit elements for a nonstroboscopic installation both bulky and expensive.

It is an object of my invention to provide a non-stroboscopic installation which is non-bulky and inexpensive as to the control circuit elements. It is an object of the invention to provide for the operation of a plurality of dephased light sources-with inductive control circuit elements of small mass as to their core elements, and low cost as to their windings. It is an object of the,

invention to provide a control circuit for a pair of de-phased fluorescent tubes which involves only two inductive windings. It is an object of the invention to provide novel means for the protection of the control circuit elements in the event of the failure of a light source, which means has the additional function of giving an unmistakable signal when the system is not operating with the proper power factor.

These and other objects of myinvention which will be set forth hereinafter, or will be appar-' ent to one skilled in the art upon reading these specifications, I accomplish in that construction and by that mode of operation of which I' shall now describe an exemplary embodiment, illustrated diagrammatically in the accompanying drawings, wherein:

Figure 1 is a diagrammatic representation of a form of my invention in which a thermostatic switch element is associated with a transformer.

Figure-2 is a diagrammatic representation of" a;

modification in which a switch responsive to anincrease inv current is located in the secondary circuit;

The power leads are indicated at I. and'Z. The lead- 1 is connected to one end of. the winding 3" of a transformer having a. core 4. This is. shown as. an autotransformer acting to increase thevoltage provided. by the power leads. l he lead 21s therefore, connected to a tap as at 5 inter-- mediate the ends of the Winding 3.

The. remaining end of the winding- 3 is provided with branch leads 6. and. 1 connected respectively-with one=end offieach ofi'the fluorescent light sources 8 and 9. The leads 6 and. 1 contain; respectively a. capacity Ii):v and. inductance I I The other ends of the light; sources 8- andv 9 are connected by. a commonlead l2 to the power: lead I. Capacities l3-:and I4 maybe connected in shunt to. the fluorescent sources 8. and 9' for the purpose of. suppressing highfrequency. surges.

In thetermfluorescent light sources I. intend toinclude all of the various types of these devices, and especially both the hot cathode and the cold cathode types. Itwill be understood that with cold cathode light sources the transformer 3', 4 Will be designed todeliver a voltage suitable for both starting and operation. With hot cathode fluorescent tubes appropriate, start-- ing circuits will be provided. These are well known in the art and are not here illustrated.

I have spoken of fluorescent light sources pri.-.

marily because suchsources, designed to, produce visible light for illumination, are those in:

the operation. of! which. a diminution of the;

stroboscopic effect isusually-desired. It; will be, understood however; that the principles of invention may be applied to enclosed; arcdevlces.

irrespective Qfi. the. presence; or absence: of fluorescent: coatinsa.

The capacity ill; acts as a. ballast for the light.

source 9.1 while the inductance l l acts as a ballast forthe light; source 3; and it-will be understood thatt-he are, dischar es'inthe two light sources are; by reason of the-differing character of these ballasts. out of phase; with each other so as to minimize the stroboscopic effect. In a typical, installation, where thevoltage. across the power leads: I ZjiS;abQlllLl1 8,VO1ts the'transformer 3. 4- may be designed to deliver approximately 350.

volts. The capacity It may have a value of twov micro-farads. The capacities l3 and I 4- may be, very much smaller-and usually. are of the. order of .005 micro-farad.

llhe; circuit is; corrected as to power factor.

Both the transformer 3, 4 and the inductance ll may be simple windings on simple cores of low mass, designed to operate properly so long as theconditionof power factor correction is maintained. In other words, I provide only enough current carrying capacity in the transformer 3, 4 to take care of the operation of the light sources 8, 9 under conditions of power factor correction. Thus the current feeding the combination of sources 8 and 9 out of the transformer is about 50% of the current required to operate either alone. It follows that if the circuit including either lamp is interrupted, the full current of the lamp has to be carried by the transformer.

In an installation such as above described, an interruption is likely to occur only through the failure of one of the light sources 8 or 9. Assuming such failure, the power factor of the circuit loses its corrected condition and the transformer 3, 4 tends to heat up. In order to protect the circuit elements in this event I provide a thermal switch IS in one of the power leads, preferably the power lead 2 where it is protected to considerable degree from the highest voltage in the system. The thermal switch includes a bimetal or other suitable temperature-actuated member and is so constructed as to open the switch contacts upon a rise in temperature. The thermal switch is locatedsoas to receive heatifrom the transformer 3, 4, and may be mounted directly on the core of that transformer or included within the same housing. When the transformer develops heat, the thermal switch opens, breaking the power circuit.

It will be evident that in my system neither lamp will operate properly if one of the lamps fails. When the thermal switch If: has broken the power circuit, the transformer 3, 4 will cool again permitting the thermal switch to close. Thus the remaining operative light source will start again, and the cycle will be repeated at intervals. This produces a flashing operation which gives a positive and unmistakable signal that something is wrong with the installation which should be corrected, as can usually be done by the replacement of the failed light source.

The transformer 3, 4 and the inductance H can be fastened together or included in the same housing, giving an especially small and inexpensive assembly of inductive control elements. Ad.- vantages of my construction are the smallness and cheapness of such an assembly, which may be employed because the thermal switch l5 protects the inductive elements from burning out under conditions of overload due to a failure of the corrected condition of the power factor. Moreover, it is not possible to operate my system for illumination improperly or with only one light source.

As a modification-to my invention, as shown in Figure 2, I may provide a thermal switch I! of the type having a heating element 18 which is responsive to increase of current and actuates the switch, in place of the switch l5. In this modification the current responsive switch may be placed in the circuit anywhere that the current increases upon disturbance of the power factor correction, such as in the lead 16 in the drawing; that is, between the high side of the auto transformer and the common connection of the working circuits. Such a switch, upon increase of the current due to the disturbance of the power factor correction, will cut out all the working circuits at short intervals and give a flickering effect to the operating lamps.

It will be understood that modifications of my invention may be made without departing from the spirit of it. While I have shown a system involving two lightsources operating out of phase with each other, more may be employed with appropriate circuit changes which the skilled worker in the art can readily make in the light of the teachings herein. If desired, a transformer having a primary and a separate secondary may be employed in place of the auto trans former herein described. Various means may be employed to cause the plurality of light sources to operate with suflicient dephasing to minimize or eliminate the stroboscopic effect, so long as the system has a corrected power factor when all light sources are operated, so long as the corrected power factor is disturbed by a failure in any one of the individual lamp circuits, and so long as there is sufficient difference between the corrected and disturbed power factor conditions to operate a switch actuated by an increase in current. Having thus descrbed my invention inan, exemplary'embodiment, what I claim as new and desire to secure by Letters Patent'is: I t

'1. In an enclosed arc installation, a. transformer, primary leads for connecting-said transformer to a source of power, secondary leadsfor connecting said transformerto enclosed are devices, a plurality of Working circuits containing enclosed are devices connected in parallel tosaid secondary leads, each such circuit containing ballast means for enclosedarc devices, certain of.

said ballast means differing from others whereby to cause arc discharges in certain of said enclosed are devices to occur otherwise than in exact phase relationship, said, transformer and said working circuits constituting a system of corrected power factor when all of said working circuits are-in operation, said transformer'having substantially only sufiicient capacityto supply. current tosaid system under conditions of power factorv correction, so as to heat up when any of said working circuits cease to operate, and means responsive to the heating up of said transformer to break the circuit in one of said primary leads. v

2. The structure claimed in claim 1 in which said transformer is an autotransformer with a core and a single winding. I I

3. The structure claimed in claim 1 in which said transformer is an autotransformer with a core and a single winding, ,and wherein said means responsive to the heating up of said transformer is a thermostatic switch in one of said primary leads in heat-transfer association with the core of said transformer. g

4-. In an enclosed arc installation, an autotransformer having a'core and a single winding,

primary leads for connecting said winding to a source of power, secondary leads for connecting said winding to enclosed are devices, a pair of, working circuits containing enclosed are devices connected in parallel to said secondary leads, one working circuit containing inductive ballast means and the other working circuit containing capacitative ballast means, said transformer and said working circuits constituting va corrected power factor system when said working circuits 4 are both in operation, and means to break the circuit of one ofsaid primary leads when the correction of said power factor is disturbed.

5. In an enclosed arc installation, an autotransformer having a core and a single winding, primary leads for connecting said winding to a source of power,'secondary leads for connecting;

said windingto enclosed arc devices, a pair-of working circuits containing enclosed are devices connected in parallel to said secondary leads, one working circuit containing inductive ballast means and the other working circuit containing capacitative ballast means, said transformer and said working circuits constituting a corrected power factor system when said working circuits are both in operation, and means to break the circuit of one of said primary leads when the correction of said power factor is disturbed, said transformer having substantially only sufficient capacity to supply current to said system under conditions of power factor correction so that said transformer will become overloaded if one of said working circuits becomes inoperative, said means to break the circuit of one of said primary leads being means thermally responsive to a heating of said transformer upon overload.

6. In an enclosed arc installation, an autotransformer having a core and a single winding, primary leads for connecting said winding to a source of power, secondary leads for connecting said winding to enclose-d are devices, a pair of working circuits containing enclosed are devices connected in parallel to said secondary leads, one Working circuit containing inductive ballast means and the other workin circuit containing capacitative ballast means, said transformer and said working circuits constituting a corrected power factor system when said working circuits are both in operation, and means to break the circuit of one of said primary leads when the correction of said power factor is disturbed, said transformer having substantially only suflicient capacity to supply current to said system under conditions of power factor correction, so that said transformer will become overloaded if one of said working circuits becomes inoperative, said means to break the circuit being a thermostatic switch in heat-exchange relationship with said transformer.

7. In an enclosed arc installation, a transformer, primary leads for connecting said transformer to a source of power, secondary leads for connecting said transformer to enclosed arc devices, a plurality of working circuits containing enclosed are devices connected in parallel to said secondary leads, each such circuit containing ballast means differing from others whereby to cause arc discharges in certain of said enclosed are devices to occur otherwise than in exact phase relationship, said transformer and said working circuits constituting a system of corrected power factor, when all of said working circuits are in operation, and means to break the circuit containing the Working circuits when the correction of said power factor is disturbed.

8. In an enclosed arc installation, a transformer, primary leads for connecting said transformer to a source of power, secondary leads for connecting said transformer to enclosed are devices, a plurality of working circuits containing enclosed are devices connected in parallel to said secondary leads, each such circuit containing ballast means differing from others whereby to cause arc discharges in certain of said enclosed are devices to occur otherwise than in exact phase relationship, said transformer and said working circuits constituting a system of corrected power factor, when all of said working circuits are in operation, and means to break the circuit containing the working circuits when the correction of said power factor is disturbed, said means comprising a thermal switch responsive to current increase.

9. In an enclosed arc installation, a transformer, primary leads for connecting said transformer to a source of power, secondary leads for connecting said transformer to enclosed arc devices, a plurality of working circuits containing enclosed are devices connected in parallel to said secondary leads, each such circuit containing ballast means differing from others whereby to cause are discharges in certain of said enclosed are devices to occur otherwise than in exact phase relationship, said transformer and said working circuits constituting a system of corrected power factor, when all of said working circuits are in operation, and means to break the circuit containing the working circuits when the correction of said power factor is disturbed, said means comprising a thermal switch responsive to current increase incorporated in one of the secondary leads.

10. In an enclosed arc installation, a transformer, primary leads for connecting said transformer to a source of power, secondary leads for connecting said transformer to enclosed are devices, a plurality of working circuits containing enclosed arc devices connected in parallel to said secondary leads, each such circuit containing ballast means differing from others whereby to cause arc discharges in certain of said enclosed are devices to occur otherwise than in exact phase relationship, said transformer and said working circuits constituting a system of corrected power factor when all of said working circuits are in operation, and a signaling means operated by the disturbance of the power factor correction.

ARNOT P. FOSTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS,

Number Name Date Re, 15,929 MacGahan Oct. '7, 1924 1,192,879 Ferrell Aug. 1, 1916 2,025,471 Osborne Dec. 24, 1935 2,223,530 Putnam Dec. 3, 1940 2,301,671 Abadie Nov. 10, 1942 2,314,311 Karash Mar. 16, 1943 

